When a pedestrian hears the screech of a car's brakes, she has to decide whether, and if so, how, to move in response. Is the action taking place blocks away, or 20 feet to the left? One of the primal mechanisms we depend on -- acting on the basis of information gathered by our sense of hearing -- is yielding its secrets. Surprising results fill in a key piece of the puzzle about how mammals act on the basis of sound cues.View full story